Fannie Mae and Freddie Mac may have lost billions of dollars as a result of banks' allegedly manipulating a benchmark that determines the price at which banks lend to one another.

The inspector general of the Federal Housing Finance Agency has concluded the companies lost more than $3 billion over a roughly two-year period starting in September 2008 on holdings of more than $1 trillion of securities and other assets tied to the London interbank offered rate, The Wall Street Journal reported Wednesday.

FHFA, the conservator for Fannie and Freddie, reportedly has begun to explore legal options against banks involved in setting Libor in response to the inspector general's findings, which were communicated in an internal memo.

An FHFA spokeswoman said in an email that FHFA "has not substantiated any particular LIBOR-related losses for Fannie Mae and Freddie Mac."

"We continue to evaluate issues associated with Libor and monitor Libor-related developments, recognizing that other federal agencies are also involved in related matters," she added.

A spokeswoman for the inspector general's office said in an email the office had "conducted a preliminary analysis of potential Libor-related losses at Fannie and Freddie and shared that with FHFA, recommending that they conduct a thorough review of the issue."

On Wednesday, UBS agreed to pay $1.5 billion to regulators in the U.S., U.K. and Switzerland to settle Libor-related investigations. In June, Barclays paid $450 million to settle charges by regulators in the U.S. and U.K. that the bank manipulated both Libor and the euro interbank offered rate.

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